These scientific papers of Richard Feynman are renowned for their brilliant content and the author's striking original style. They are grouped by topic: path integral approach to the foundations of quantum mechanics and quantum held theory, renormalized quantum electrodynamics, theory of superfluid liquid helium, theory of the Fermi interaction, polarons, gravitation, partons, etc. Feynman's Princeton PhD thesis appears in print for the first time. Comments are provided by the editor, together with biographical notes and an annotated bibliography of Feynman and his work.